This invention relates to a method for recovering polymer resins from solution. More particularly, it relates to a process for isolating a polymer resin from a liquid-liquid dispersion that is formed by admixing an aqueous fluid with an organic solvent that contains the dissolved polymer.
Several methods are currently used to recover polymer resins from solution. Some of the methods are energy intensive and require large quantities of steam to accomplish removal of the solvent. Other methods require high viscosity process equipment which require a high investment cost. Further, the residual solvent contained in the product powder or particles is difficult to remove.
U.S. Pat. No. 4,546,172 discloses the production of polycarbonate resin particles having high bulk density that are produced by a process in which a polymer solution, or polymer solution-water mixture are fed into an agitation tank containing water the temperature of which is higher than the boiling point of the solvent methylene chloride. The methylene chloride evaporates and the polycarbonate is recovered in the form of an aqueous slurry. This process has the disadvantage that the polycarbonate often agglomerates, producing a large sticky mass prior to precipitation, leading to difficulties in processing. In the process described above, an off-tank wet pulverizer is used to grind the large sticky mass of polycarbonate produced upon evaporation of the methylene chloride.
In another polymer isolation scheme the polymer solution is added to a non-solvent resulting in the precipitation of the polymer. The polymer is then collected. This technique necessitates the use of large quantities of the non-solvent and ultimately the separation of the non-solvent solvent mixture. Moreover, a portion of the product polymer may be soluble in the non-solvent solvent mixture occasioning loss of product.
The utilization of high viscosity process equipment is another solution to the problem of agglomeration.
It would be desirable to develop a process for the recovery of polymers in solution which avoids the use of high shear agitation in the solvent removal step and large quantities of non-solvent, and minimizes energy consumption and the use of special equipment. The present invention overcomes these limitations on the recovery of polymers from organic mixtures.